Ferrite with constricted magnetic hysteresis loop



0. ECKERT June 20, 1961 FERRITE WITH CONSTRICTED MAGNETIC HYSTERESISLOOP \Mn 2 0 H AYAYAYAYY AVA 4 YAVAVA \AA/km AMA A W I A/V v AVA 45W/W AAA MMA A A/ United States Patent Gfice 2,989,474 Patented June 20, 19612,989,474 FERRI'IE WITH CONSTRICIED MAGNETIC HYSTERESIS LOOP OskarEckert, L'auf (Pegnitz), Germany, assignor t Ste'atit-MagnesiaAktiengesellschaft, Lani (Pegnrtz), Germany, a corporation of GermanyFiled Oct. 18, 1956, Sen-No. 616,818 Claims priority, applicationGermany Oct. 29, 1955 4 Claims. (Cl. 252-625) Ferromagnetic metals withconstricted hysteresis loops (see, for example, Bozorth, Ferromagnetism,by Nostrand Co., Inc., 1951, pages 498 to 499), have, as is well known,at small field strength within the constriction area, constantpermeability, i.e., permeability independent of the field strength equalto the initial permeability, very low hysteresis losses and, in general,small residual losses. As indicated in the above cited literature, suchmaterials may be subjected to thermo-magnetic .treatment. Bythermomagnetic treatment, in this connection, is meant the passing thrua thermic cycle during the simultaneous presence ofa magneticlongitudinal or transverse field. The concept of longitudinal ortransverse field is, in this connection, to be understood as relative tothe later measuring field; a longitudinal or transverse field,respectively, means that such field, during the thermomagnetictreatment, is parallel, respectively vertical, to the later measuringfield. Thru this type of treatment, these ferromagnetic materialsdisplay a substantial alteration of the form of the hysteresis loop, andhence a change of the magnetic properties.

This invention is based on the discovery that it is possible to makespecific ferrites showing a constricted magnetic hysteresis loop whichare, consequently, capable of thermomagnetic treatment similarly as formetals.

The invention teaches the production of such ferrites of themanganese-nickel ferrite system which can be subjected to thermomagnetictreatment of the above type, and are distinguished from hithertofamiliar ferrites by the fact that, under the same manufacturingconditions, they have constricted hysteresis loops.

In accordance with the invention, ferrites with this characteristic inthe manganese-nickel-fenite system must have a composition of at least50 mol-percent Fe O and a small addition of cobalt oxide. The additionof cobalt oxide is suitably determined between 0.1 and 5% by weight,calculated on the total basic batch of the manganese-nickel ferrite,expressed in metallic oxides. The invention has shown that it isparticularly advantageous to choose the cobalt oxide content between0.35 and 1.5% by weight, calculated on the basic batch. Themanganesenickel-ferrites in question, which react strongly to theaddition of cobalt oxide with a constricted loop, cover, in thethree-component system Fe O -Mn O -NiO, the area defined in the attacheddiagram (FIG. 3) by the quadrangle A, B, C, D. The compositions at thecorners in percent by Weight (see FIG. 3), are:

FezOz M11201 N 5 tween 1250 C. and 1380 C. To produce the constrictedhysteresis loop in ferrites, in accordance with invention, it isnecessary that the cooling takes place slowly, particularly in thetemperature range between 700 C. and room temperature. The cooling speedis dependent upon the volume of the fired body. As a criterion, it maybe stated that for a ring of about 46 mm. outside diameter, 34 mm.inside diameter, and 10 mm. height; the cooling time from 700 C. to roomtemperature should take not less than 12 hours. If the rings are cooledrapidly, the effect of loop constrictiondoes not occur. However, theconstriction may be regained even for rings cooled too rapidly, byre-heating them to a temperature of about 700 C., and cooling themslowly, as above described.

An example of the invention follows hereafter:

In a steel ball mill are ground together 412.5 g. F8203, 37.5 g. M11 050 g. NiO, 3.25 g. C00. After 6 hours ,of grinding, the slip is pouredthrough a 4900 mesh screen (4900 meshes per square cm.) into a porcelaindish, and dried. The powder thus obtained is pressed, according toceramic pressing techniques, into rings having dimensions of 59 mm.outside diameter, 35.8 mm. inside diameter, and 12 mm. height, theamount of pressure applied being about 0.5 to 1 t./cm. The ferritepieces, thus obtained, are sintered in a kiln at 1350" C. for two hours,whereupon the heat is shut off. The rings are cooled to room temperaturein the kiln during a period of approximately 24 hours. The ferrite ringsthus obtained are provided with 0.4 mm. copper enameled wire withwindings as primary winding, and, as secondary winding, further 200windings with 0.2 mm. copper enameled wire are applied. Theoscillographic photograph of this ferrite, produced in accordance withthe invention, is shown in FIG. 1, one can distinctly recognize the loopconstriction of the hysteresis loop.

The following experiment proves that fern'tes produced in accordancewith the invention are susceptible to thermomagnetic treatment:

.The ferrite toroid as prepared in the example, with 100 windings as aprimary winding, is placed in a kiln. While heating to 600 C., and slowcooling for 12 hours to room temperature, a longitudinal magnetic fieldis maintained by means of the ring winding by 1 a. direct current,corresponding to a magnetic field strength of a about 15 a.-windings/cm.If the hysteresis loop of the fenrite after this thermomagnetictreatment is recorded in the same manner as described above, the resultis analogous to that of metals when they are subjected to heat treatmentin the longitudinal magnetic field; a complete change of the form of thehysteresis loop takes place, as may be seen in Fig. 2. In analogousmanner, heat treatment in the transverse magnetic field may be carriedout with corresponding effect; (see the above cited I book by Bozorth).

The technical progress obtained with such ferrites in accordance withthe invention, may be seen in the following: with thermic longitudinalmagnetization, for example, fem'tes with distinctly rectangularhysteresis loop may be produced which are of importance to the entirefields of electronics and for magnetic amplification, for telephone andhigh-frequency fields; with thermic cross magnetization, ferrites ofhigh quality and a permeability independent of field strength may beproduced, which are particularly suitable for the field oftelecommunication.

I claim:

1. A process of making a cobalt-modified manganese nickel ferrite with aconstricted hysteresis loop which ferrite responds to thermomagnetictreatment to alter the hysteresis loop characteristics comprisingproviding an intimately mixed powder composition consisting essentiallyof 71 to 90% by Weight of ferric oxide, 0.1 to 5% by weight of cobaltoxide and about 10% to about 2 9% by weight of metal oxides selectedfrom the group consisting of Mn O NiO and mixtures of M11 and NiO, theproportion of said oxides being selected so that the Fe O is at least 50mol percent of the entire mixture when the Mn O content is calculated asMnO, molding the resultant powder composition to shape and firing atabout 1250 C. to 1380 C., and thereafter slowly cooling the firedproduct from a temperature of 700" C. down to room temperature over aperiod of at least about 12 hours.

2. The process as claimed in claim 1 in which the cobalt content isbetween 0.35 and 1% by weight of the composition.

3. A shaped and fired, cobalt-modified ferrite body of themanganese-nickel ferrite system having a constricted hysteresis loop,said ferrite being responsive to thermomagnetic treatment to alter thehysteresis loop characteristics, said ferrite containing 71 to 90% byweight of ferric oxide, from about 10% to about 29% by weight ofmanganese oxide, calculated as Mn O 0.1 to 5% by weight of cobalt oxide,the remainder consisting essentially of NiO, the proportion of saidoxides being selected so that the ferric oxide is at least mol percentof the entire composition, said fired product being prepared by theprocess of claim 4.

4. The ferrite as claimed in claim 3 in which the cobalt content isbetween 0.35 and 1% by weight of the composition.

References Cited in the file of this patent UNITED STATES PATENTS2,549,089 Hegyi Apr. 17, 1951 2,723,239 Harvey Nov. 8, 1955 2,736,708Crowley Feb. 28, 1956 2,882,236 Gorter et a1 Apr. 14, 1959 2,886,530Greger May 12, 1959 FOREIGN PATENTS 735,375 Great Britain Aug. 17, 19551,117,385 France Feb. 20, 1956 1,125,577 France July 16, 1956 OTHERREFERENCES Economos: J. Amer. Ceramic 800., July 1955, page 242.

Weil: Comptes Rendus v. 234, pp. 1351, 1352, March 1952.

Bozorth et al.: Physical Review, Sept. 15, 1955, pages 1788-1798,particularly page 1792.

R.C.A. Review, September 1950, vol. 11, No. 3, pages 321-363, page 345pertinent.

3. A SHAPED AND FIRED, COBALT-MODIFIED FERRITE BODY OF THEMANGANESE-NICKEL FERRITE SYSTEM HAVING A CONSTRICTED HYSTERESIS LOOP,SAID FERRITE BEING RESPONSIVE TO THERMOMAGNETIC TREATMENT TO ALTER THEHYSTERESIS LOOP CHARACTERISTICS, SAID FERRITE CONTAINING 71 TO 90% BYWEIGHT OF FERRIC OXIDE, FROM ABOUT 10% TO ABOUT 29% BY WEIGHT OFMANGANESE OXIDE, CALCULATED AS MN2O3, 0.1 TO 5% BY WEIGHT OF COBALTOXIDE, THE REMAINDER CONSISTING ESSENTIALLY OF NIO, THE PROPORTION OFSAID OXIDES BEING SELECTED SO THAT THE FERRIC OXIDE IS AT LEAST 50 MOLPERCENT OF THE ENTIRE COMPOSITION, SAID FIRED PRODUCT BEING PREPARED BYTHE PROCESS OF CLAIM 4.